U.S. patent application number 15/341246 was filed with the patent office on 2017-12-07 for direct current magnetoresistive jog offset compensation.
This patent application is currently assigned to SEAGATE TECHNOLOGY LLC. The applicant listed for this patent is SEAGATE TECHNOLOGY LLC. Invention is credited to Qiang BI, Mingzhong DING, Xiong LIU, Xiang LU, Kian Keong OOI.
Application Number | 20170352371 15/341246 |
Document ID | / |
Family ID | 57484008 |
Filed Date | 2017-12-07 |
United States Patent
Application |
20170352371 |
Kind Code |
A1 |
DING; Mingzhong ; et
al. |
December 7, 2017 |
DIRECT CURRENT MAGNETORESISTIVE JOG OFFSET COMPENSATION
Abstract
Systems and methods for compensating for magnetoresistive (MR)
jog offset direct current (DC) drift in a disc drive are described.
In one embodiment, a method may include determining an occurrence
of NOS, for example, by monitoring disc slip, to determine when the
method should proceed. An MR jog offset DC drift amount is
determined for each head of the disc drive. One of several
approaches may be employed for determining the MR jog offset DC
drift amount. By determining an MR jog offset DC drift amount for
each head, a compensation profile is determined for the drive. The
determined compensation profile may then be used during operation
of the disc drive to compensate for the DC drift. One of several
approaches may be employed for compensating based on the
compensation profile.
Inventors: |
DING; Mingzhong; (Singapore,
SG) ; LIU; Xiong; (Singapore, SG) ; LU;
Xiang; (Singapore, SG) ; BI; Qiang;
(Singapore, SG) ; OOI; Kian Keong; (Singapore,
SG) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SEAGATE TECHNOLOGY LLC |
Cupertino |
CA |
US |
|
|
Assignee: |
SEAGATE TECHNOLOGY LLC
Cupertino
CA
|
Family ID: |
57484008 |
Appl. No.: |
15/341246 |
Filed: |
November 2, 2016 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
15170859 |
Jun 1, 2016 |
9520149 |
|
|
15341246 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G11B 5/59694 20130101;
G11B 5/59627 20130101 |
International
Class: |
G11B 5/596 20060101
G11B005/596 |
Claims
1. A storage device comprising: a non-operating shock (NOS)
detector to determine an occurrence of NOS based at least in part
on slip of at least one storage disc; an MR jog offset direct
current (DC) drift detector to determine a magnetoresistive (MR)
jog offset DC drift amount based at least in part on a variable
read performed on the at least one storage disc when the NOS
detector has determined the occurrence of NOS; and an MR jog offset
compensator to compensate for the determined MR jog offset DC drift
amount using the determined DC MR jog offset.
2. The storage device of claim 1, further comprising at least one
MR read/write head that performs the variable read on the at least
one storage disc.
3. The storage device of claim 1, comprising: a plurality of
storage discs comprising a data storage medium; a plurality of MR
read/write heads, each of the plurality of MR read/write heads
associated with a respective one of the plurality of storage discs,
the MR jog offset DC drift detector to determine a plurality of MR
jog offset DC drift amounts based on a corresponding plurality of
variable reads, each of the plurality of variable reads using a
respective one of the plurality of MR read/write heads, each of the
determined plurality of MR jog offset DC drift amounts
corresponding to the respective one of the plurality of MR
read/write heads; and a correction profile determiner to determine
a correction profile based at least in part on the determined
plurality of MR jog offset DC drift amounts, the correction profile
comprising a plurality of DC MR jog offsets corresponding to the
plurality of MR read/write heads, the MR jog offset compensator to
compensate for the determined plurality of MR jog offset DC drift
amounts using the determined correction profile.
4. The storage device of claim 1, the MR jog offset compensator to
compensate for the determined MR jog offset DC drift amount using
write seek feedforward compensation.
5. The storage device of claim 1, the MR jog offset compensator to
compensate for the determined MR jog offset DC drift amount by
migrating data using shingled magnetic recording (SMR) band rewrite
operation (BRO).
6. The storage device of claim 1, the variable read comprising a
read from the group consisting of: a spiral read, a zig-zag read,
and a sinusoidal read.
7. The storage device of claim 1, the variable read comprising a
plurality of reads performed with different track offsets of the at
least one MR read/write head.
8. The storage device of claim 1, the MR jog offset direct current
(DC) drift detector to determine the MR jog offset DC drift amount
based at least in part on a measurement from the group consisting
of: a bit error rate (BER) measurement and a variable gain
adjustment measurement.
9. An apparatus comprising: an MR jog offset direct current (DC)
drift detector to determine an MR jog offset DC drift amount based
at least in part on a variable read of a data storage medium based
at least in part on an occurrence of non-operating shock; and a
correction profile determiner to determine a DC MR jog offset based
at least in part on the determined MR jog offset DC drift
amount.
10. The apparatus of claim 9, further comprising: an MR jog offset
compensator to compensate for the determined MR jog offset DC drift
amount using write seek feedforward compensation or by migrating
data using shingled magnetic recording (SMR) band rewrite operation
(BRO) based at least in part on the determined DC MR jog
offset.
11. The apparatus of claim 9, the variable read performed over at
least one revolution of at least one disc of the data storage
medium using at least one MR read/write head.
12. The apparatus of claim 11, the variable read comprising a
plurality of reads performed with different track offsets of the at
least one MR read/write head.
13. The apparatus of claim 9, the MR jog offset direct current (DC)
drift detector to determine the MR jog offset DC drift amount based
at least in part on a measurement from the group consisting of: a
bit error rate (BER) measurement and a variable gain adjustment
measurement.
14. A method comprising: determining magneto-resistive (MR) jog
offset direct current (DC) drift amount associated with an
occurrence of non-operating shock (NOS) in a disc drive;
determining a correction profile based at least in part on the MR
jog offset DC drift amount.
15. The method of claim 14, further comprising: compensating for MR
jog offset DC drift using the correction profile.
16. The method of claim 15, compensating for the MR jog offset DC
drift comprising: performing write seek feedforward compensation or
migrating data using a shingled magnetic recording (SMR) band
rewrite operation (BRO).
17. The method of claim 15, determining the MR jog offset DC drift
amount comprising: writing data to a test track on a surface of a
disc of the disc drive; and determining a change between a new
center of the written data and a previous center of data written to
the test track.
18. The method of claim 17, determining the change comprising:
performing a spiral read of the test track over one revolution of
the disc to obtain sector-wise bit error rate (BER) or variable
gain adjustment (VGA) values; and determining a highest BER value
of the sector-wise BER measurement values or a lowest VGA value of
the sector-wise VGA values to identify the MR jog offset DC drift
amount.
19. The method of claim 18, determining the correction profile
comprising: obtaining MR jog offset DC correction values by
repeating the spiral read and identification of the MR jog offset
DC drift amount on a plurality of test tracks across the surface of
the disc for each individual head.
20. The method of claim 17, determining the change comprising:
performing a zig-zag read of the test track over one revolution of
the disc to obtain a plurality of sector-wise bit error rate (BER)
or variable gain adjustment (VGA) values for each sector; averaging
the plurality of sector-wise BER or VGA values for each sector; and
determining a highest BER value of the averaged sector-wise BER
values or a lowest VGA value of the averaged VGA values to identify
the MR jog offset DC drift amount.
Description
RELATED APPLICATION
[0001] This application is a continuation of U.S. patent
application Ser. No. 15/170,859, filed on 1 Jun. 2016 and entitled
DIRECT CURRENT MAGNETORESISTIVE JOG OFFSET COMPENSATION, pending,
the disclosure of which is incorporated in its entirety by this
reference.
SUMMARY
[0002] The present disclosure is directed to methods and systems
for compensating for changes in magnetoresistive (MR) jog offset in
a disc drive. In some embodiments, the present systems and methods
may compensate for MR jog offset DC drift resulting from
non-operating shock (NOS).
[0003] A storage device for MR jog offset compensation is
described. In one embodiment, the storage device may include a data
storage medium comprising at least one disc, at least one
magnetoresistive (MR) read/write head associated with the at least
one disc, a non-operating shock (NOS) detector to determine an
occurrence of NOS based at least in part on slip of the at least
one disc, an MR jog offset direct current (DC) drift detector to
determine an MR jog offset DC drift amount based at least in part
on a variable read performed over at least one revolution of the at
least one disc using the at least one MR read/write head when the
NOS detector has determined the occurrence of NOS, and an MR jog
offset compensator to compensate for the determined MR jog offset
DC drift amount using the determined DC MR jog offset for the at
least one MR read/write head.
[0004] In some embodiments, the data storage medium may include a
plurality of discs and the at least one MR read/write head may
comprise a plurality of MR read/write heads, each of the plurality
of MR read/write heads being associated with a respective one of
the plurality of discs. In some cases, the MR jog offset DC drift
detector is to determine a plurality of MR jog offset DC drift
amounts based on a corresponding plurality of variable reads, each
of the plurality of variable reads using a respective one of the
plurality of MR read/write heads, each of the determined plurality
of MR jog offset DC drift amounts corresponding to the respective
one of the plurality of MR read/write heads. In some
configurations, the storage device further includes a correction
profile determiner to determine a correction profile based at least
in part on the determined plurality of MR jog offset DC drift
amounts. The correction profile may be a plurality of DC MR jog
offsets corresponding to the plurality of MR read/write heads. The
MR jog offset compensator may compensate for the determined
plurality of MR jog offset DC drift amounts using the determined
correction profile.
[0005] In some embodiments, the MR jog offset compensator
compensates for the determined MR jog offset DC drift amount using
write seek feedforward compensation. In other embodiments, the MR
jog offset compensator compensates for the determined MR jog offset
DC drift amount by migrating data using shingled magnetic recording
(SMR) band rewrite operation (BRO).
[0006] In some embodiments, the variable read may be a spiral read,
a zig-zag read, a sinusoidal read, or some combination thereof. In
other embodiments, the variable read may be a plurality of reads
performed with different track offsets of the at least one MR
read/write head.
[0007] In some embodiments, the MR jog offset direct current (DC)
drift detector determines the MR jog offset DC drift amount based
at least in part on a bit error rate (BER) measurement. In other
embodiments, the MR jog offset direct current (DC) drift detector
determines the MR jog offset DC drift amount based at least in part
on a variable gain adjustment measurement.
[0008] An apparatus for MR jog offset compensation is also
described. In one embodiment, the apparatus may include an MR jog
offset direct current (DC) drift detector to determine an MR jog
offset DC drift amount based at least in part on a variable read
performed over at least one revolution of at least one disc of a
data storage medium using at least one MR read/write head based at
least in part on an occurrence of non-operating shock, and a
correction profile determiner to determine a DC MR jog offset for
the at least one MR read/write head based at least in part on the
determined MR jog offset DC drift amount.
[0009] A method for MR jog offset compensation is also described.
In one embodiment, the method may include determining an occurrence
of non-operating shock (NOS) in a disc drive by monitoring disc
slip, determining magneto-resistive (MR) jog offset direct current
(DC) drift amount associated with the occurrence of NOS,
determining a correction profile based at least in part on the MR
jog offset DC drift amount, and compensating for MR jog offset DC
drift using the correction profile.
[0010] The foregoing has outlined rather broadly the features and
technical advantages of examples according to this disclosure so
that the following detailed description may be better understood.
Additional features and advantages will be described below. The
conception and specific examples disclosed may be readily utilized
as a basis for modifying or designing other structures for carrying
out the same purposes of the present disclosure. Such equivalent
constructions do not depart from the scope of the appended claims.
Characteristics of the concepts disclosed herein--including their
organization and method of operation--together with associated
advantages will be better understood from the following description
when considered in connection with the accompanying figures. Each
of the figures is provided for the purpose of illustration and
description only, and not as a definition of the limits of the
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] A further understanding of the nature and advantages of the
present disclosure may be realized by reference to the following
drawings. In the appended figures, similar components or features
may have the same reference label. Further, various components of
the same type may be distinguished by following a first reference
label with a dash and a second label that may distinguish among the
similar components. However, features discussed for various
components--including those having a dash and a second reference
label--apply to other similar components. If only the first
reference label is used in the specification, the description is
applicable to any one of the similar components having the same
first reference label irrespective of the second reference
label.
[0012] FIG. 1 is a block diagram of an example of a system in
accordance with various embodiments;
[0013] FIGS. 2A and 2B show a slider and a disc and illustrate
geometry related to MR jog offset in accordance with various
aspects of this disclosure;
[0014] FIG. 3 shows a block diagram of an example of a module in
accordance with various aspects of this disclosure;
[0015] FIG. 4 is a flow chart illustrating an example of a method
in accordance with various aspects of this disclosure; and
[0016] FIG. 5 is a flow chart illustrating an example of another
method in accordance with various aspects of this disclosure.
DETAILED DESCRIPTION
[0017] The following relates generally to MR jog offset
compensation in a disc drive. A disc drive typically includes one
or more read/write heads that are driven relative to a storage
medium to write data to and read data from the medium. During
production of a disc drive, once the drive has been assembled, an
MR jog offset will be calibrated for the drive, for example, during
a certification process. For each read-write head of the disc
drive, a set of polynomial coefficients, a.sub.0, a.sub.1, a.sub.2
. . . , an, are determined and saved, for example, to non-volatile
storage. For a given track x on a particular disc, the MR jog
offset D(x) for the associated head is obtained as follows:
D(x)=a.sub.0x.sup.n+a.sub.1x.sup.n-1+ . . . +a.sub.n
[0018] After certification, however, the MR jog offset may incur DC
shift or drift. DC shift may occur, for example, as a result of
non-operating shock (NOS) to the disc drive. For a mobile drive, a
typical NOS specification is 1000G @ 2 ms. When a disc drive is
subjected to such a high G level shock, certain mechanical
components will be shifted or drifted. Note that the description
herein uses the term drift to encompass both drift and shift.
[0019] Regardless of the cause of the drift, in one embodiment, the
present disclosure describes an efficient method to compensate for
MR jog offset DC drift in a disc drive. In the case of NOS induced
drift, the method may include determining an occurrence of NOS, for
example, by monitoring disc slip, to determine when the method
should proceed.
[0020] In either case, an MR jog offset DC drift amount is
determined for each head of the disc drive. As described further
below, one of several approaches may be employed for determining
the MR jog offset DC drift amount. By determining an MR jog offset
DC drift amount for each head, a compensation profile is determined
for the drive. The determined compensation profile is then used
during operation of the disc drive to compensate for the DC drift.
As described further below, one of several approaches may be
employed for compensating based on the compensation profile.
[0021] FIG. 1 is a block diagram illustrating one embodiment of a
data storage system 100 (e.g., a disc drive system) in which the
present systems and methods may be implemented. The data storage
system 100 includes media 106, such as a plurality of discs 107,
which are mounted on a spindle motor 140 by a clamp 108 (also
referred to as a spindle or spindle component). Each surface of the
media 106 has an associated slider 110, which carries a read/write
head 111 for communication with the media surface. Sliders 110 are
supported by suspensions and track accessing arms of an actuator
mechanism 116. For example, the actuator mechanism 116 can be of
the type known as a rotary moving coil actuator and includes a
voice coil motor (VCM) 118. The VCM 118 rotates actuator mechanism
116 about a pivot shaft to position sliders 110 over a desired data
track along an arcuate path between an inner diameter (ID) and an
outer diameter (OD) of respective discs 107. The VCM 118 is driven
by electronic circuitry based on signals generated by the
read/write heads 111 and a servo controller 138.
[0022] As previously discussed, media 106 can include a plurality
of discs 107. Each disc 107 has a plurality of substantially
concentric circular tracks. Each track is subdivided into a
plurality of storage segments. As defined herein, a storage segment
is the basic unit of data storage in media 106. Each storage
segment is identified and located at various positions on media
106. In the disc-type media example, storage segments or data
sectors are "pie-shaped" angular sections of a track that are
bounded on two sides by radii of the disc and on the other side by
the perimeter of the circle that defines the track. Each track has
related logical block addressing (LBA). LBA includes a cylinder
address, head address and sector address. A cylinder identifies a
set of specific tracks on the disc surface to each disc 107 which
lie at equal radii and are generally simultaneously accessible by
the collection of read/write heads 111. The head address identifies
which head can read the data and therefore identifies which disc
from the plurality of discs 107 the data is located. As mentioned
above, each track within a cylinder is further divided into sectors
for storing data and servo information. The data sector is
identified by an associated sector address.
[0023] The data storage system 100 includes a system processor 136,
which is used for controlling certain operations of data storage
system 100 in a known manner. The various operations of data
storage system 100 are controlled by system processor 136 (e.g.,
storage controller) with the use of programming and/or instructions
stored in a memory 137. The data storage system 100 also includes a
servo controller 138, which generates control signals applied to
the VCM 118 and spindle motor 140 (as well as the microcontroller,
not shown). The system processor 136 instructs the servo controller
138 to seek read/write head 111 to desired tracks. The servo
controller 138 is also responsive to servo data, such as servo
burst information recorded on disc 107.
[0024] The data storage system 100 further includes a preamplifier
(preamp) 142 for generating a write signal applied to a particular
read/write head 111 during a write operation, and for amplifying a
read signal emanating from a particular read/write head 111 during
a read operation. A read/write channel 144 receives data from the
system processor 136, via a buffer 144, during a write operation,
and provides encoded write data to the preamplifier 142. During a
read operation, the read/write channel 146 processes a read signal
generated by the preamplifier 142 in order to detect and decode
data recorded on the discs 107. The decoded data is provided to the
system processor 136 and ultimately through an interface 148 to a
host computer 150.
[0025] In some configurations, the data storage system 100 may
include a DC drift compensator, such as a DC MR jog offset
compensation module 130. In one example, the data storage system
100 may be a component of a host (e.g., operating system, host
hardware system, etc.). The DC MR jog offset compensation module
130 may compensate for DC drift of the read/write heads 111, for
example, by feedforward of a correction factor during write
operation to maintain the writer at the original written-in data
center. Alternatively, the DC MR jog offset compensation module 130
may compensate for DC drift of the read/write heads 111 by
migrating data using shingled magnetic recording (SMR) band rewrite
operations.
[0026] FIG. 2A shows a block diagram 200-a illustrating a slider
110-a in accordance with various aspects of this disclosure. As
shown, the slider 110-a includes a read head 111r and a write head
111w, corresponding to the MR read/write head 111 shown in FIG. 1,
for example. The read head 111r and the write head 111w are
separated and offset from each other. As shown in FIG. 2A, the
separation between the read head 111r and the write head 111w is S,
which may be referred to as the R/W separation. The offset between
the read head 111r and the write head 111w is 0, which may be
referred to as the R/W offset. This physical separation and offset
of the read head 111r and the write head 111w results in a
particular MR jog offset across the surface of an associated
disc.
[0027] FIG. 2B shows a block diagram 200-b illustrating a disc
107-a in accordance with various aspects of this disclosure. The
disc 107-a may have a plurality of tracks on its surface, with a
track 107t being shown for reference. The disc 107-a is mounted on
a spindle 108-a, as described above with reference to FIG. 1.
Further, an actuator (not shown) having a pivot 116p is configured
to move a slider (not shown) relative to the disc 107-a. The slider
may be configured as shown in FIG. 2A, for example.
[0028] The slider includes a read head 111r-a and a write head
111w-a, as illustrated in FIG. 2B. As further depicted in FIG. 2B,
an MR jog offset O.sub.MRj for the MR read/write head (read head
111r-a and 111w-a) is determined based on one or more of R/W offset
O, R/W separation S, a distance D.sub.PS between the actuator pivot
116p and a center 108c of the spindle 108-a, a distance D.sub.PH
between the actuator pivot 116p and the MR read/write head (e.g.,
the read head 111r-a), and a radius R.sub.t of the track 107t.
[0029] As discussed above, a disc drive may experience a NOS that
drifts various mechanical components of the drive. For example, the
actuator pivot may drift relative to the spindle pivot (center).
With the geometrical relationship illustrated in FIG. 2B, the MR
jog offset O.sub.MRj will incur DC drift. Also, for example, a top
cover of the disc drive may drift and cause a tilt in the actuator.
In such case, a top (closer to the cover) slider (e.g., MR write
head) associated with a top disc will incur worse MR jog offset DC
drift than a bottom slider associated with a bottom disc.
[0030] The impact of such a DC drift may be disastrous for the disc
drive. For example, new data write operations after the NOS may
cause DC encroachment that may corrupt the data written on an
adjacent track before the NOS. With such encroachment, one or more
data sectors may report an uncorrectable data error (UDE) when an
attempt to read the data on the adjacent track is made. As the
tracks per inch (TPI) on a disc is increased, addressing the
problem of DC drift may increase in importance.
[0031] FIG. 3. shows a block diagram 300 of a DC MR jog offset
compensation module 130-a. The DC MR jog offset compensation module
130-a may include one or more processors, memory, and/or one or
more storage devices. The DC MR jog offset compensation module
130-a may include an NOS determination module 305, a DC drift
determination module 310, and a DC drift compensator module 315.
Each of these components may be in communication with each other.
The DC MR jog offset compensation module 130-a may be one example
of the DC MR jog offset compensation module 130 of FIG. 1.
[0032] As described herein, the NOS determination module 305 is
configured to determine when an NOS has occurred. Determination of
a NOS occurrence may be used to determine when to proceed with DC
drift determination and compensation. Although any suitable
approach for determining NOS may be employed, the NOS determination
module 305 may determine when an NOS has occurred by monitoring
disc slip. For example, the NOS determination module 305 may employ
the existing servo system of the disc drive, such as the system
processor 136 and/or the servo controller 138 shown in the example
of FIG. 1. The servo system may be configured to monitor
alternating current feed-forward (ACFF) to detect occurrence of
NOS. When a disc is not subjected to NOS, the data tracks are
concentric and there is no AC component in the VCM current to
follow a data track. However, if there is disc slip due to NOS, the
data tracks become eccentric and there will be a sinusoidal
component in the VCM to follow one of the data tracks. The
amplitude of the ACFF is proportional to the amount of disc
slip.
[0033] The DC drift determination module 310 is configured to
determine an amount of DC drift incurred by each MR read/write head
(or slider) in the disc drive. Although various details for
determining the amount of DC drift are described, it should be
understood that the amount of DC drift may be determined or
otherwise obtained in any suitable manner. As described further
below, the DC drift determination module 310 determines the amount
of DC drift for each slider/head using at least one test track on a
disc associated with the slider/head. For example, one or more test
tracks across the surface of the disc may be laid out and prepared
(e.g., during the certification process for the disc drive), which
are reserved and not used for data storage. To determine the amount
of DC drift after NOS, a new write operation is performed to the
prepared test tracks. The new write data will reflect the MR jog DC
drift. A subsequent read back operation (multiple read, spiral
read, zig-zag read, etc.) is be used to determine the DC shift
based on BER or RVGA.
[0034] In general, bit error rate (BER) is a function of an amount
of the reader (e.g., read head) being off-track, wherein a larger
off-track of the reader corresponds to a lower BER. In the case of
an MR jog offset DC shift occurring, the relationship between the
BER (e.g., raw sector) and the reader off-track amount (e.g.,
percent track position) correspondingly shifts. As such, the DC
drift determination module 310 can determine the DC shift amount by
measuring cross-track BER of the test track, with the highest BER
corresponding to the DC drift amount.
[0035] Alternatively, the DC drift determination module 310 can
determine the DC shift amount based on the relationship between
read variable gain adjustment (read VGA or VGAR) and the reader
off-track amount. In this case, the DC drift determination module
310 can determine the DC shift amount by measuring cross-track VGAR
of the test track, with the lowest VGAR corresponding to the DC
drift amount.
[0036] For either the BER or the VGA approach, several techniques
may be employed. For the sake of brevity and clarity, the following
techniques are discussed with respect to BER. However, it should be
understood that each of these techniques may be employed for the
VGA approach as well.
[0037] A first technique is to perform multiple reads, each with a
different reader offset (e.g., from negative to positive), to
measure BER and obtain BER values for each offset. The DC drift
amount is then determined as the offset corresponding to the
highest BER value. A potential downside to this technique is the
multiple reads at different track offset for each slider/head,
which may be relatively time-consuming and could negatively impact
performance of the disc drive.
[0038] A second technique is to perform a spiral read by
positioning the reader progressively over a range of offsets (e.g.,
from an original (pre-drift/pre-NOS) offset minus fifty percent
(D-50%) to the original offset plus fifty percent (D+50%) during
one revolution of the disc. This can be achieved, for example, by
adjusting to different set point values for different servo
sectors. As such, the spiral read technique can achieve a
relatively quick sector-wise BER measurement, from which the
highest BER and corresponding offset is determined to determine the
DC drift amount.
[0039] More particularly, to read from negative fifty percent
(-50%) off-track to fifty percent (50%) off-track, the position set
point for a given sector m is X+D+C(m), with C(m) calculated as
follows:
C ( m ) = - 50 % + 100 % N m ##EQU00001##
where N is the total number of servo sectors. By disabling read
retry, a relationship between sector-wise BER and data sector l is
obtained from reading over one revolution of the disc. In general,
the relationship between data sector l and servo sector m is
predetermined, for example, by a read/write (R/W) zone table for
the disc drive. The foregoing equation maps servo sector m to a
physical off-track amount C. A second order polynomial fit of BER
to off-track amount C is given by:
BER=a*C.sup.2+b*C+c
[0040] The off-track amount C.sub.x corresponding to the highest
BER is given by:
C x = - b 2 a , ##EQU00002##
where C.sub.x is the MR jog offset DC drift amount C for test track
x.
[0041] Repeating the above on all test tracks across the whole
surface of each disc for each respective slider/head obtains DC
shift values that can be used to populate a DC MR jog offset
correction table for each slider/head, which can be saved to
non-volatile storage of the disc drive, for example, for use in
future write operations (e.g., feedforward correction, discussed
below). The DC MR jog offset correction values can still be in the
form of polynomial coefficients, b.sub.0, b.sub.1, b.sub.2 . . . ,
b.sub.n, similar to the original calibrated/certification MR jog
offset values for a given track x on a particular disc, the MR jog
offset correction value C(x) for the associated head is obtained as
follows:
C(x)=b.sub.0x.sup.n+b.sub.1x.sup.n-1+ . . . +b.sub.n
[0042] Additional techniques, similar to the second technique, may
involve a zig-zag movement of the reader or a sinusoidal movement
of the reader, for example, through +/-50% track offset, to obtain
multiple reads per sector over one revolution of the disc. Thus,
multiple sector wise BER measurements are obtained for each track
offset. The multiple measurements are then averaged to obtain a
single BER value for each sector. As above, the offset
corresponding to the highest BER value is the MR jog offset DC
drift amount.
[0043] Once the DC drift amount has been determined for each
slider/head of the disc drive), the DC drift compensator module 315
determines a correction factor or MR jog offset adjustment value
for compensating the positioning of each slider/head for future
read/write operations. For a disc drive including multiple discs
and associated sliders/heads, the correction factors/adjustment
values for the sliders/heads may be stored (e.g., in memory 137) as
a correction profile. The correction profile is then accessed for
read/write commands (according to the particular disc to be read
from/written to) to properly position the appropriate
slider/head.
[0044] As described further below, the correction profile may be
employed using feedforward during write operation, i.e., using the
compensation value C(x) during write operation as a feedforward
value to the reader position, in order to place the writer to the
center of the original written-in data path to avoid off-track
encroachment. During read operation, the original MR jog table
D(x), obtained during CERT process to place the reader to the
written-in data path, is used to retrieve data. Alternatively, for
a data migration approach using BRO, the compensation value C(x) is
not used during write operation, and the new data path will be with
some offset (e.g., in the amount of C(x)) from the original
written-in data path. For this case, the compensation value C(x) is
used in conjunction with D(x) (i.e., D(x)-C(x)) when later
attempting to read back the "newly" written data. Only D(x) is used
to retrieve "old" written data.
[0045] The DC drift compensator module 315 may use the correction
profile in any suitable manner to compensate for the DC shift, for
example, to avoid data encroachment on adjacent tracks. For
example, the DC drift compensator module 315 can adjust the
positioning of the read head during write operations by feedforward
of the correction factor/offset adjustment value C(x) into the
servo position set point. In such a manner, the write head is
positioned to the original (pre-drift/pre-NOS) position for a given
track. For read operations, the original (e.g., certification
process) MR jog offset D(x) is used.
[0046] As an alternative, the DC drift compensator module 315 can
use full band rewrite operation (BRO) to write a whole shingled
magnetic recording (SMR) band. During the BRO, the servo position
set point remains at the original center of the particular track.
Thus, the newly written data is shifted away from the original data
center of the track by the corresponding correction
factor/adjustment value C(x). When writing according to the shingle
direction, the whole band is shifted by the correction
factor/adjustment value. Because of a fat track or a fat track and
a guard band situated between bands according to SMR, the write
operation for a last track of a band will not cause encroachment to
the first track of the adjacent band. However, for a correction
factor/adjustment value that is significantly large (e.g., such
that encroachment on the next band is likely to occur), the data of
the first track(s) of the adjacent band may be read back into a
data buffer before performing the full BRO in the preceding SMR
band.
[0047] For each new write operation after NOS, a full BRO for the
band to which the data track belongs should be performed.
Additionally, the SMR bands should be tracked with respect to the
BRO--keeping track of which SMR bands have been subjected to BRO
and which have not. To read back original data (e.g., data that was
written before the drift/NOS), the original (pre-drift/pre-NOS) MR
jog offset D(x)-C(x) is used. Alternatively, or additionally,
original data may be corrected (e.g., in background tasks) by
reading the original data from a band back into a data buffer, and
then re-writing using a full BRO for the whole band. Also, SMR band
usage may be monitored and recorded, so that, if data was never
written to a particular SMR band before the DC drift/NOS, the SMR
band can be skipped for data migration.
[0048] One or more of the components of the DC MR jog offset
compensation module 130-a, individually or collectively, may be
implemented using one or more application-specific integrated
circuits (ASICs) adapted to perform some or all of the applicable
functions in hardware. Alternatively, the functions may be
performed by one or more other processing units (or cores), one or
more integrated circuits, or combinations thereof. In other
examples, other types of integrated circuits may be used (e.g.,
Structured/Platform ASICs, Field Programmable Gate Arrays (FPGAs),
and other Semi-Custom ICs), which may be programmed in any manner
known in the art. The functions of each module may also be
implemented--in whole or in part--with instructions embodied in
memory formatted to be executed by one or more general and/or
application-specific processors.
[0049] FIG. 4 is a flow chart illustrating an example of a method
400 for DC MR jog offset compensation in a disc drive, in
accordance with various aspects of the present disclosure. One or
more aspects of the method 400 may be implemented in conjunction
with the data storage system 100 of FIG. 1, the subassemblies of
FIGS. 2A-2B, and/or the DC MR jog offset compensation module 130-a
of FIG. 3. In some examples, a storage device may execute one or
more sets of codes to control the functional elements of the
storage device to perform one or more of the functions described
below. Additionally or alternatively, the storage device may
perform one or more of the functions described below using
special-purpose hardware.
[0050] At block 405, the method 400 may include determining an
occurrence of non-operating shock (NOS). Determining the NOS
occurrence at block 405 may be performed in any suitable manner,
such as described above with reference to FIG. 3. As illustrated by
the dotted line of block 405, such operation(s) may be optional,
for example, to be performed at startup of the disc drive when the
method 400 is to address DC MR jog offset compensation due to
NOS.
[0051] At block 410, the method 400 may include determining an MR
jog offset DC drift amount. For example, the operation(s) at block
410 may involve performing any one of the techniques described
above with reference to FIG. 3.
[0052] Next at block 415, the method 400 may include determining a
correction profile for multiple sliders/heads of the disc drive.
For example, the operation(s) at block 415 may involve obtaining
multiple offset values for each slider/head from performance of the
operation(s) at block 410 on a per track basis. In other words, a
correction profile may be obtained for each head, with the
correction value being calculated on a per track basis. Once
determined, the correction profile can be stored locally at the
disc drive.
[0053] Then at block 420, the method 400 may include compensating
for MR jog offset DC drift. For example, the operation(s) at block
410 may involve performing either of the BER or the VGA approaches
described above with reference to FIG. 3. As illustrated by the
dotted line of block 420, such operation(s) may be optional. In
some cases, the method 400 may end with the operation(s) at block
415. For example, if no write operations occur after the NOS and
before a subsequent NOS, no compensation for the MR jog offset
drift may be performed (e.g., in the case of the feedforward
correction approach discussed above). In the case of the SMR BRO
approach discussed above, proactive correction of original data may
be performed, with or without write operations occurring after the
NOS and before a subsequent NOS.
[0054] The operation(s) at block 405-420 may be performed using the
DC MR jog offset compensation module 130 described with reference
to FIGS. 1 and 2 and/or another module. Thus, the method 400 may
provide for DC MR jog offset compensation in a disc drive that
experiences DC drift due to NOS or other reasons. It should be
noted that the method 400 is just one implementation and that the
operations of the method 400 may be rearranged, omitted, and/or
otherwise modified such that other implementations are possible and
contemplated.
[0055] FIG. 5 is a flow chart illustrating an example of another
method 500 for DC MR jog offset compensation in a disc drive, in
accordance with various aspects of the present disclosure. More
specifically, the method 500 may be employed to implement
particular approaches described herein. One or more aspects of the
method 500 may be implemented in conjunction with the data storage
system 100 of FIG. 1, the subassemblies of FIGS. 2A-2B, and/or the
DC MR jog offset compensation module 130-a of FIG. 3. In some
examples, a storage device may execute one or more sets of codes to
control the functional elements of the storage device to perform
one or more of the functions described below. Additionally or
alternatively, the storage device may perform one or more of the
functions described below using special-purpose hardware.
[0056] At block 505, the method 500 may include determining an
occurrence of non-operating shock (NOS). Determining the NOS
occurrence at block 405 may be performed in any suitable manner,
such as described above with reference to FIG. 3. The method 500
may be considered to be specific to DC MR jog offset compensation
for DC drift caused by NOS.
[0057] At block 510, the method 500 may include performing a
variable read of a test track over one revolution of a particular
disc. The variable read at block 510 may be performed in any
suitable manner, such as described above with reference to FIG. 3.
At block 515, the method 500 may include averaging sector-wise BER
values obtained from the operation(s) at block 510. As illustrated
by the dotted line of block 515, such operation(s) may be optional.
In some cases, the operations at block 510 may involve obtaining
multiple reads per sector over one revolution of the disc (e.g.,
zig-zag or sinusoidal movement of the reader). In such cases, the
method 500 may include the averaging operation(s) at block 515. In
other embodiments, the operations at block 510 may involve
obtaining a single read per sector or offset (e.g., N revolutions
each read at different offset or spiral movement of the reader over
one revolution), which would not require the averaging operation(s)
at block 515.
[0058] At block 520, the method 500 may include determining the
highest BER value from the results of the variable read
operation(s) at block 510, with or without the averaging
operation(s) at block 515. As discussed above, the offset
corresponding to the highest BER may be used as the DC drift
amount. The method 500 may continue to block 525, at which a
determination may be made as to whether any sliders/heads remain
for which the DC drift is to be determined. If so, the method 500
may return to block 510 to repeat operations for a subsequent
slider/head. If not (e.g., the DC drift amount(s) for each
slider/head are determined), the method 500 may continue to block
530, at which the method 500 may include performing write seek
forward compensation based at least in part on the determined DC
drift amount(s) for the particular slider/head for each write
operation occurring after the NOS.
[0059] The operations at blocks 505-530 may be performed using the
DC MR jog offset compensation module 130 described with reference
to FIGS. 1 and 2 and/or another module. Thus, the method 500 may
provide for DC MR jog offset compensation in a disc drive that
experiences DC drift due to NOS as described herein. It should be
noted that the method 500 is just one implementation and that the
operations of the method 500 may be rearranged, omitted, and/or
otherwise modified such that other implementations are possible and
contemplated.
[0060] In some examples, aspects from the methods 400 and 500 may
be combined and/or separated. It should be noted that the methods
400 and 500 are just example implementations, and that the
operations of the methods 400 and 500 may be rearranged or
otherwise modified such that other implementations are
possible.
[0061] The detailed description set forth above in connection with
the appended drawings describes examples and does not represent the
only instances that may be implemented or that are within the scope
of the claims. The terms "example" and "exemplary," when used in
this description, mean "serving as an example, instance, or
illustration," and not "preferred" or "advantageous over other
examples." The detailed description includes specific details for
the purpose of providing an understanding of the described
techniques. These techniques, however, may be practiced without
these specific details. In some instances, known structures and
apparatuses are shown in block diagram form in order to avoid
obscuring the concepts of the described examples.
[0062] Information and signals may be represented using any of a
variety of different technologies and techniques. For example,
data, instructions, commands, information, signals, bits, symbols,
and chips that may be referenced throughout the above description
may be represented by voltages, currents, electromagnetic waves,
magnetic fields or particles, optical fields or particles, or any
combination thereof.
[0063] The various illustrative blocks and components described in
connection with this disclosure may be implemented or performed
with a general-purpose processor, a digital signal processor (DSP),
an ASIC, an FPGA or other programmable logic device, discrete gate
or transistor logic, discrete hardware components, or any
combination thereof designed to perform the functions described
herein. A general-purpose processor may be a microprocessor, but in
the alternative, the processor may be any conventional processor,
controller, microcontroller, and/or state machine. A processor may
also be implemented as a combination of computing devices, e.g., a
combination of a DSP and a microprocessor, multiple
microprocessors, one or more microprocessors in conjunction with a
DSP core, and/or any other such configuration.
[0064] The functions described herein may be implemented in
hardware, software executed by a processor, firmware, or any
combination thereof. If implemented in software executed by a
processor, the functions may be stored on or transmitted over as
one or more instructions or code on a computer-readable medium.
Other examples and implementations are within the scope and spirit
of the disclosure and appended claims. For example, due to the
nature of software, functions described above can be implemented
using software executed by a processor, hardware, firmware,
hardwiring, or combinations of any of these. Features implementing
functions may also be physically located at various positions,
including being distributed such that portions of functions are
implemented at different physical locations.
[0065] As used herein, including in the claims, the term "and/or,"
when used in a list of two or more items, means that any one of the
listed items can be employed by itself, or any combination of two
or more of the listed items can be employed. For example, if a
composition is described as containing components A, B, and/or C,
the composition can contain A alone; B alone; C alone; A and B in
combination; A and C in combination; B and C in combination; or A,
B, and C in combination. Also, as used herein, including in the
claims, "or" as used in a list of items (for example, a list of
items prefaced by a phrase such as "at least one of" or "one or
more of") indicates a disjunctive list such that, for example, a
list of "at least one of A, B, or C" means A or B or C or AB or AC
or BC or ABC (e.g., A and B and C).
[0066] In addition, any disclosure of components contained within
other components or separate from other components should be
considered exemplary because multiple other architectures may
potentially be implemented to achieve the same functionality,
including incorporating all, most, and/or some elements as part of
one or more unitary structures and/or separate structures.
[0067] Computer-readable media includes both computer storage media
and communication media including any medium that facilitates
transfer of a computer program from one place to another. A storage
medium may be any available medium that can be accessed by a
general purpose or special purpose computer. By way of example, and
not limitation, computer-readable media can comprise RAM, ROM,
EEPROM, flash memory, CD-ROM, DVD, or other optical disc storage,
magnetic disc storage or other magnetic storage devices, or any
other medium that can be used to carry or store desired program
code means in the form of instructions or data structures and that
can be accessed by a general-purpose or special-purpose computer,
or a general-purpose or special-purpose processor. Also, any
connection is properly termed a computer-readable medium. For
example, if the software is transmitted from a website, server, or
other remote source using a coaxial cable, fiber optic cable,
twisted pair, digital subscriber line (DSL), or wireless
technologies such as infrared, radio, and microwave, then the
coaxial cable, fiber optic cable, twisted pair, DSL, or wireless
technologies such as infrared, radio, and microwave, or any
combination thereof, are included in the definition of medium.
Disc, as used herein, include compact disc (CD), laser disc,
optical disc, digital versatile disc (DVD), floppy disc and Blu-ray
disc where discs usually reproduce data magnetically, while discs
reproduce data optically with lasers. Combinations of the above are
also included within the scope of computer-readable media.
[0068] The previous description of the disclosure is provided to
enable a person skilled in the art to make or use the disclosure.
Various modifications to the disclosure will be readily apparent to
those skilled in the art, and the generic principles defined herein
may be applied to other variations without departing from the scope
of the disclosure. Thus, the disclosure is not to be limited to the
examples and designs described herein but is to be accorded the
broadest scope consistent with the principles and novel features
disclosed.
[0069] This disclosure may specifically apply to security system
applications. This disclosure may specifically apply to storage
system applications. In some embodiments, the concepts, the
technical descriptions, the features, the methods, the ideas,
and/or the descriptions may specifically apply to storage and/or
data security system applications. Distinct advantages of such
systems for these specific applications are apparent from this
disclosure.
[0070] The process parameters, actions, and steps described and/or
illustrated in this disclosure are given by way of example only and
can be varied as desired. For example, while the steps illustrated
and/or described may be shown or discussed in a particular order,
these steps do not necessarily need to be performed in the order
illustrated or discussed. The various exemplary methods described
and/or illustrated here may also omit one or more of the steps
described or illustrated here or include additional steps in
addition to those disclosed.
[0071] Furthermore, while various embodiments have been described
and/or illustrated here in the context of fully functional
computing systems, one or more of these exemplary embodiments may
be distributed as a program product in a variety of forms,
regardless of the particular type of computer-readable media used
to actually carry out the distribution. The embodiments disclosed
herein may also be implemented using software modules that perform
certain tasks. These software modules may include script, batch, or
other executable files that may be stored on a computer-readable
storage medium or in a computing system. In some embodiments, these
software modules may permit and/or instruct a computing system to
perform one or more of the exemplary embodiments disclosed
here.
[0072] This description, for purposes of explanation, has been
described with reference to specific embodiments. The illustrative
discussions above, however, are not intended to be exhaustive or
limit the present systems and methods to the precise forms
discussed. Many modifications and variations are possible in view
of the above teachings. The embodiments were chosen and described
in order to explain the principles of the present systems and
methods and their practical applications, to enable others skilled
in the art to utilize the present systems, apparatus, and methods
and various embodiments with various modifications as may be suited
to the particular use contemplated.
* * * * *